The invention particularly pertains to an end cap for small electric motors, usually of the direct current type, wherein an end cap is mounted upon the end of a metal motor casing. In particular, the invention is directed to the features of the end cap for reducing cost, simplifying assembly and improving operation and dependability.
Small electric motors often include armature brushes associated with, or located within, an end cap mounted upon the end of the motor casing. The design and construction of brush holders is significant in reducing the cost of the electric motor, and simplifying motor assembly, and examples of motor brush structure for small electric motors are shown in the assignee's U.S. Pat. Nos. 3,791,684 and 3,792,298.
To reduce costs and improve motor assembly techniques, it is known to form the motor end cap of a dielectric synthetic plastic material by an injection molding procedure, and an example of such a construction is shown in the assignee's U.S. Pat. No. 4,209,723.
In the constructions shown in the aforementioned patents, the brushes are mounted upon a brush card separate from the end cap, and the brush cards consist of a plurality of brush holders separately assembled to a dielectric card or support. In these patented devices the use of a separate brush card increases manufacturing costs and complicates motor assembly.
An object of the invention is to provide a molded dielectric synthetic plastic end cap for electric motors wherein brush holders and guides are homogeneously defined on the end cap of the material thereof.
It is also an object of the invention to provide a molded dielectric synthetic plastic end cap for electric motors wherein a brush holder and guide is defined on the end cap by homogeneous cantilevered fingers capable of being deformed for frictionally gripping the brush to hold the brush in a retracted position during assembly of the end cap to a motor armature.
An additional object of the invention is to provide a molded dielectric synthetic plastic motor end cap having retainers defined therein for guiding and receiving electrical conductors and maintaining the electrical conductors at right angles relative to an access opening defined in the end cap wherein an effective conductor anchoring and strain relief is achieved simply by inserting the conductors into the retainers as the conductors are assembled to the end cap.
Yet another object of the invention is to provide a molded dielectric synthetic plastic end cap having a homogeneous circuit breaker retainer defined thereon permitting a circuit breaker to be readily assembled to the end cap and maintained thereon by a positive holding force.
A further object of the invention is to provide a molded dielectric synthetic plastic end cap for an electric motor wherein the end cap is held to the motor by tie bolts extending through ears formed on the end cap, and the ears are of such configuration as to cooperate with the motor casing to resist deflection and bending as the tie bolts are tightened.
In the practice of the invention the entire end cap for a small electric motor is molded by injection molding and formed of a dielectric synthetic plastic material of relatively rigid characteristics. The end cap includes ears having holes defined therein through which tie bolts extend for maintaining the end cap upon the associated motor casing, and the ears include an axially extending portion closely overlapping and engaging a portion of the motor casing in an axial direction whereby the configuration of the ears causes the portions of the ears overlapping the motor casing to be radially deflected inwardly upon the motor casing as the tie bolts are tightened, and engagement of the ears with the motor casing minimizes ear deflection and permits relatively high tie bolt tension without damage to the end cap.
The end cap includes an inner surface disposed toward the motor casing interior, and a plurality of projections and configurations homogeneously extend from this inner surface for defining brush holding apparatus, strain relief means for motor electric conductors, and a retainer for a circuit breaker which protects the motor against electrical overload.
The end cap includes a central recess for receiving a bearing which rotatably supports one end of the motor armature, and spaced about the bearing are a plurality of sets of brush retaining fingers. Each brush set consists of two fingers of dielectric synthetic plastic material homogeneously extending from the end cap inner side and each having a free cantilevered end. The fingers of a set are parallel and spaced from each other having an inner configuration defining a guide for reciprocally receiving a conventional electric motor brush.
A spring anchor also homogeneously extends from the material of the motor cap in alignment with a brush guide defined by a pair of fingers, the anchor being located at the end of the brush guide remote from the end cap armature bearing, and unattached with respect to the associated fingers.
A slot is defined between the set of fingers at their free ends wherein the brush conductor may extend therethrough, and as the fingers are only supported at the end cap, the free ends of the fingers, and the portions of the fingers adjacent to the free ends, are capable of being deformed toward each other so as to frictionally grip a brush located therebetween. Forked clamps, or similar tools, may be used to deform the fingers of an associated set toward each other to hold the brush in a retracted position during assembly of the end cap to the armature. The natural resiliency of the fingers restores the dimension of the brush guide to its original shape after the deforming tools are released permitting the associated brush to freely reciprocate within the defined guide, and a coil compression spring interposed between the brush and the associated spring anchor biases the brush into engagement with the motor armature.
A notch is formed in the periphery of the end cap for receiving the electrical conductors required to supply electricity to the motor. Conductor retainers in the form of ribs are defined within the end cap adjacent the conductor notch for receiving the conductors, or conductor connectors, and the conductor retainers are of such configuration that the portion of the conductors received within the retainers are at right angles to the conductor portions extending through the end cap, and this relationship provides excellent conductor strain relief resisting tension forces imposed upon the conductors, and preventing such tension from being transferred to the brush conductors, or the circuit breaker conductor, located within the end cap.
The end cap configuration also includes a cantilevered hook homogeneously extending from the cap inner surface having a shoulder defined at its outer end in spaced relationship to a cradle or bed defined in the end cap. The configuration of the hook and cradle is such as to permit a small circuit breaker to be inserted therebetween and retained on the end cap by the hook shoulder. As the hook is resiliently deflectable it may be momentarily deflected away from the cradle to permit insertion of the circuit breaker, but the resilient nature of the hook assures dependable circuit breaker retention during motor operation.
The construction of an electric motor molded end cap utilizing the aforementioned features reduces the cost of the end cap, simplifies assembly of the brushes, springs, conductors and circuit breaker into the end cap, simplifies assembly of the end cap to the motor casing, while providing a more dependable end cap with respect to the electrical, assembly and handling characteristics.